Tender: Try some interrupts. Interrupting spores before they explode, interrupting deathly swarn, etc. Set some AoE on the monks. It's vital to pound as hard as you can on this stuff from the get go, before they've got time to get into their 'dormant husk' state. After that, it's a lot tougher.
Also, *lots* of hex removal is never a bad thing for this dungeon. Sure, run a WoH/Prot monk, but also take a monk running PnH and spotless mind, etc. Hexes are the 'meta' down there, you need to be prepared for em, heh.
pblock!+CoF! Gwen would be good, as the AI is usually quicker at interrupts.
You've got ranger + derv, right? Also might consider a rit hero running support... something like: [Offering of Spirit], [Destruction], [Ancestors' Rage], [Splinter Weapon], [Strength of Honor], [Warmonger's Weapon], [Remove Hex], Rez (FOMF/Rez chant, etc). 12 smite. 14 channeling. That'll make your derv a happy happy dervish, and put some pressure on the plants.
So you've got: You (ranger), Monk, Gwen, MM + Dervish (monk/rit/insert some AoE here).
On my MM heroes, when facing areas with a lot of hexes, I give them [Resilient Weapon] and they're not half bad with it. You get extra armor when hexed + health regen, so everyone is happy.
It's worth a shot
I never leave home without my splinter rit when on melee >_> Whee, numbers!